Wireless receiver and wireless reception method

ABSTRACT

A Multi-Input/Multi-Output (MIMO) receiver may include a plurality of receiving antennas that receive a plurality of radio signals and an estimation section that finds channel estimation values of the plurality of radio signals. A MIMO separation section separates, using a MIMO scheme, the plurality of radio signals in accordance with the channel estimation values, and a compensation section compensates for channel variations of the plurality of radio signals. A selection section selects one of the MIMO separation section and the compensation section.

This application is a continuation of application Ser. No. 10/536,010filed May 23, 2005, which is a 371 application of PCT/JP2003/015059 andwhich is based on Japanese Patent Application No. 2002-341741 filed onNov. 26, 2002, all the disclosure of each of the above applicationsbeing incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a wireless receiver which receives datatransmitted in parallel from a plurality of transmitting antennas with aplurality of receiving antennas, and a wireless reception methodemployed in such an apparatus.

BACKGROUND ART

In recent years, Multi-Input/Multi-Output (MIMO) communication has beendrawing an attention as a technology for enabling a communication ofmassive data such as images. In the MIMO communication, differenttransmitted data (sub streams) are respectively transmitted from aplurality of antennas in a transmitter side, and a plurality of thetransmitted data that are mixed in a propagation path are separated intothe respective original transmitted data in a receiver side by using apropagation path estimate (see, for example, Japanese Patent Laid-OpenNo. 2002-44051 (FIG. 4)).

In an actual operation, in the MIMO communication, signal transmittedfrom a transmission apparatus is received with the antennas, the numberof which is equal to or larger than the number of the transmissionapparatuses, and the propagation path characteristics between antennasare estimated based on pilot signals, which are respectively insertedinto signals received with the respective antennas. This estimatedpropagation path characteristic H is represented by a matrix of 2×2,where, for example, number of the transmitting antennas is two andnumber of the receiving antenna is two. In the MIMO communication, basedon an inverse matrix of the obtained propagation path characteristic Hand received signals obtained with respective receiving antennas,transmission signals (sub streams) transmitted by respectivetransmitting antennas are found.

With reference to FIG. 1A, principle of the MIMO communication will bedescribed for a case where the number of antennas of a transmitter 10and that of a receiver 20 are respectively two. Here, signalstransmitted via antennas 11 and 12 of the transmitter 10 are representedas TX1 and TX2, respectively, and signals received via antennas 21, 22of the receiver 20 are represented as RX1 and RX2, respectively.

With this assumption, the received signals (RX1, RX2) can be expressedwith (equation 1) shown in FIG. 1B. Here, A represents a propagationpath characteristic between the transmitting antenna 11 and thereceiving antenna 21, B represents a propagation path characteristicbetween the transmitting antenna 12 and the receiving antenna 21, Crepresents a propagation path characteristic between the transmittingantenna 11 and the receiving antenna 22, and D represents a propagationpath characteristic between the transmitting antenna 12 and thereceiving antenna 22.

Thus, as for the antenna 21 and 22 of the receiver 20, the signal isreceived in a form of a mixed combination of TX1 and TX2, as expressedin (equation 1). In order to separate TX1 and TX2, for example, eitherone of TX1 and TX2 is defined as a desired signal component and theother is defined as an interference signal component, and theinterference signal component should be compensated.

In order to remove (compensate) the interference signal component statedabove and to obtain the transmission signal (TX1, TX2) from the receivedsignal, an inverse matrix of a matrix consisting of these fourpropagation path characteristics A, B, C and D is found as expressed in(equation 2). Therefore, the transmitter 10 transmits the signalcontaining a known signal for propagation path estimation (pilot signal,for example) inserted in the transmission signal, and the receiver 20conducts a propagation path estimation based on this known signal toobtain the propagation path characteristics A, B, C and D, therebyfinding the above-described inverse matrix.

Procedures for actually finding the transmission signal (TX1, TX2) fromthe received signal (RX1, RX2) includes: a Zero-Forcing (ZF) arithmeticoperation for separating a sub stream (respective data) by using only aninverse matrix arithmetic operation presented by (equation 2), orMinimum Mean Square Error (MMSE) arithmetic operation for separating soas to minimize an error, and the like.

As such, in the MIMO communication, a plurality of signals, which havebeen transmitted at the same time at the same frequency, can betheoretically separated respectively in the receiver, and thus thecommunication at higher rate with higher capacity becomes possible.

However, since there is an influence such as an inter-code interferencedue to a noise or a multipath in an actual apparatus, and/or since thereis also a quantization error or the like in an actual circuitry, aninterference compensation error is generated in the process ofcompensating for an interference signal component from the transmissionsignal, and there is a problem that error rate characteristic in thereceiving side significantly deteriorates when this error is larger. Inaddition, depending on the propagation environment, a value of adeterminant |AD−BC| of the inverse matrix represented in FIG. 1B(equation 2) may be closer to zero, and since the conventional apparatusattempts to compensate for the interference signal component even insuch situation, another problem occurs that an interference compensationerror in the separated desired signal becomes greater, therebysignificantly deteriorating the error rate in the receiving side.

DISCLOSURE OF INVENTION

An object of the present invention is to improve an error ratecharacteristic in the receiving side even under the environment, inwhich an interference compensation error becomes larger in the receivingside, when different data are transmitted between a plurality oftransmitting antennas and a plurality of receiving antennas respectivelyas in the MIMO communication.

This object is achieved by providing a wireless receiver that receivesdifferent data transmitted via wireless from a plurality of transmittingantennas using a plurality of receiving antenna, comprises a propagationpath compensation section that conducts a propagation path compensation(channel variation compensation) of a received signal, and aninterference compensation section that conducts a compensation(separation and removal) of an interference signal component, whereinone of these sections are suitably selected to be employed depending ona situation.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic diagram for describing a principle of a MIMOcommunication.

FIG. 1B includes equations that represent a relationship of transmissionsignals and received signals.

FIG. 2 is a block diagram, illustrating a configuration of a wirelessreceiver according to first embodiment of the present invention.

FIG. 3 is a block diagram, illustrating an internal structure of acontroller section according to first embodiment of the presentinvention.

FIG. 4 is a flow chart, describing an operation of the controllersection according to first embodiment of the present invention.

FIG. 5 is a schematic diagram for specifically describing anadvantageous effect obtainable by the wireless receiver according tofirst embodiment of the present invention.

FIG. 6 is a block diagram, illustrating a variation of the wirelessreceiver according to first embodiment of the present invention.

FIG. 7 is a block diagram, illustrating a configuration of a controllersection of a wireless receiver according to with second embodiment ofthe present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in reference tothe annexed figures as follows. While the description is made inreference to a case of, for example, performing a MIMO communication byusing two antennas for either of the transmitting and receiving sides,respectively, the present invention can also be applied for a casehaving an arbitrary number of antennas.

First Embodiment

FIG. 2 is a block diagram, illustrating a configuration of a wirelessreceiver according to a first embodiment of the present invention.

A wireless receiver shown in FIG. 2 comprises receiving antennas 101,receiving sections 102, a propagation path compensation section 103, aninterference compensation section 104, a controller section 105, aselecting section 106, a demodulating section 107 and a decoding section108.

In FIG. 2, a receiving section 102-1 performs a predetermined wirelessreceiving processing such as a down-converting and the like over asignal that is received through a receiving antenna 101-1, and thenoutput thereof to the propagation path compensation section 103 and theinterference compensation section 104. Similarly, a receiving section102-2 performs a predetermined wireless receiving processing such as adown-converting and the like over a signal that is received through areceiving antenna 101-2, and then output thereof to the propagation pathcompensation section 103 and the interference compensation section 104.

The propagation path compensation section 103 performs propagation pathestimations (channel estimations) for the signals output from thereceiving sections 102-1 and 102-2, and a propagation path compensation(channel variation compensation) is conducted on the basis of theresults, and then the resultant signals are output to the selectingsection 106. Here, the “propagation path estimation” means estimating amagnitude of a propagation path variation (channel variation) influencedby fading or the like in a propagation path after the radio signal istransmitted from the transmitting side till arriving at the receivingantenna of the receiving side. Also, the “propagation path compensation”means, for example, complex-multiplying a predetermined vector into theoriginal signal in order to remove (compensate) the influence of thepropagation path variation based on the results of the propagation pathestimation (channel estimation value).

The interference compensation section 104 performs similar propagationpath estimation for the signals output from the receiving sections102-1, 102-2 as the propagation path compensation section 103 performsand output this results to the controller section 105, and also performsthe previously explained MIMO separation processing and output theseparated received signals to the selecting section 106.

The selecting section 106 selects one of the signals output from thepropagation path compensation section 103 and the interferencecompensation section 104 under the control of the controller section105, and output thereof to a demodulating section 107. The details ofthe control conducted by the controller section 105 will be discussedlater.

The demodulating section 107 performs a predetermined demodulatingprocessing for the signal output from the selecting section 106corresponding to a modulation system such as Quadrature Phase ShiftKeying (QPSK), 16 Quadrature Amplitude Modulation (16QAM) used in thetransmitting side, and output the processed signal to a decoding section108.

The decoding section 108 performs a predetermined decoding processingfor the demodulated signal output from the demodulating section 107corresponding to a coding manner used in the transmitting side to obtaina received signal.

FIG. 3 is a block diagram, illustrating an internal structure of thecontroller section 105. The controller section 105 comprises an absolutevalue calculation section 111, a subtraction section 112 and acomparative judgement section 113.

The result of the propagation path estimation, which is output from theinterference compensation section 104, includes a desired signalcomponent and an interference signal component, as mentioned above. Theabsolute value calculation section 111-1 calculates an absolute value ofthe desired signal component in the result of the propagation pathestimation output from the interference compensation section 104, andoutput thereof to the subtraction section 112. Similarly, the absolutevalue calculation section 111-2 calculates an absolute value of theinterference signal component in the result of the propagation pathestimation output from the interference compensation section 104, andoutput thereof to the subtraction section 112.

The subtraction section 112 subtracts the absolute value of theinterference signal component (output of the absolute value calculationsection 111-2) from the absolute value of the desired signal component(output of the absolute value calculation section 111-1), and output theobtained difference to the comparative judgement section 113.

Comparative judgement section 113 compares the difference output fromthe subtraction section 112 with a predetermined threshold, andinstructs (outputs a control signal C1 to) the selecting section 106 toselect an output of the interference compensation section 104 when thedifference is smaller than the threshold. In addition, when differenceis equal to or larger than the threshold, the control signal C1 isoutput to the selecting section 106 so as to select the output of thepropagation path compensation section 103.

Next, operations of the controller section 105 having theabove-described configuration will be described in reference to a flowchart shown in FIG. 4.

The desired signal component of the result of the propagation pathestimation output from the interference compensation section 104 isinput into the absolute value calculation section 111-1 (ST1010). TheAbsolute value calculation section 111-1 calculates an absolute value ofthe result of the propagation path estimation (ST1020). Similarly, theinterference signal component of the result of the propagation pathestimation output by the interference compensation section 104 is inputinto the absolute value calculation section 111-2 (ST1030). The absolutevalue calculation section 111-2 calculates an absolute value of theresult of the propagation path estimation (ST1040).

The subtraction section 112 finds a difference between the absolutevalue of the desired signal component and the absolute value of theinterference signal component (ST1050). Incidentally, the calculateddifference indicates how relatively large the propagation path variationgenerated in the desired signal component is, as compared with thepropagation path variation generated in the interference signalcomponent. Thus, larger difference indicates that the propagation pathvariation generated in the desired signal component is larger than thepropagation path variation generated in the interference signalcomponent.

Comparative judgement section 113 compares the difference output fromthe subtraction section 112 with a predetermined threshold (ST1060), andoutputs an instruction (control signal) to the selecting section 106 toselect an output of the interference compensation section 104 when thedifference is smaller than the threshold (ST1070).

In addition, when difference is equal to or larger than the threshold,the instruction (control signal) is output to the selecting section 106so as to select the output of the propagation path compensation section103 (ST1080). More specifically, the operation is performed that, whenthe level of the propagation path variation generated in the desiredsignal component is equivalent to the level of the propagation pathvariation generated in the interference signal component, a signal,which is processed by the separation processing via a MIMO technique, isselected, and when the level of the propagation path variation generatedin the interference signal component is much smaller than the level ofthe propagation path variation generated in the desired signalcomponent, a signal, which is processed by a simple propagation pathcompensation, is selected.

While it is illustrated here that two inputs are included in thecontroller section 105 in order to simplify the description, four inputsare actually included in the controller section 105 as described above,since the desired signal component and the interference signal componentof the result of the propagation path estimation exist in respectivereceiving antennas. In this occasion, for example, if every two inputscorresponding to respective receiving antennas are handled via a timedivision, two results of the threshold determination can be obtained. Insuch case, in either of the determination results, the output of thepropagation path compensation section 103 may be selected only in thecase where the difference calculated in the subtraction section 112 isequal to or higher than the threshold. In addition, each of thedetermination results may be reflected for every receiving antenna. Morespecifically, the operation may be performed, in which the signalprocessed by the propagation path compensation processing is selected asthe signal received by the receiving antenna 101-1, and the signalprocessed by interference compensation processing is selected as thesignal received by the receiving antenna 101-2.

In addition, while the description is presented by illustrating the caseof calculating the difference between the absolute values of thepropagation path compensation values of the desired signal and theinterference signal and comparing the difference thereof with thethreshold, ratio of absolute values of propagation path estimate of thedesired signal and the interference signal, respectively, that is,(absolute value of the propagation path estimate of the desiredsignal)/(absolute value of the propagation path estimate of theinterference signal) may be calculated, and the obtained ratio may becompared with the threshold. However, a benefit of presenting smallerscale of the hardware can be provided when the procedure for utilizingthe difference is selected.

In addition, the controller section 105 output the control signal C2 tothe interference compensation section 104 so as to stop the rest of theinterference compensation processing except for the propagation pathestimation processing, when the propagation path compensation section103 is selected. Having this configuration, since the electric powerconsumed by the interference compensation section 104 is considerablylarge, an effect of cutting the power consumption can be expected. Here,it is needless to say that, when the interference compensation section104 is selected, a function for instructing a stop to the propagationpath compensation section 103 may be installed.

Next, advantageous effects obtainable by the wireless receiver havingthe above-described configuration will be specifically described byusing FIG. 5.

In FIG. 5, a wireless receiver 100 according to the present embodimentreceives radio signals transmitted by a wireless transmission apparatus150 having two transmitting antennas 151-1 and 151-2 via, receivingantennas 101-1 and 101-2.

However, as illustrated by the solid lines in the figure, the radiosignal transmitted from the transmitting antenna 151-1 directly arriveat the receiving antenna 101-1 and 101-2, due to an absence of anyobstacle in the midway of the propagation path. On the other hand, asillustrated by the dotted lines in the figure, the radio signaltransmitted from the transmitting antenna 151-2 does not directlyarrive, or arrives with considerably weakened signal strength, at thereceiving antenna 101-1 and 101-2, due to an existence of a building 160in the midway of the propagation path.

In general, even if the fact that the radio signal is transmittedthrough multipath is considered, it can easily be supposed that theradio signal transmitted from the transmitting antenna 151-1 is receivedin the receiver side at stronger signal intensity than the signalintensity, at which the radio signal transmitted from the transmittingantenna 151-2 is received. In such circumstances, in MIMO communication,for example, it may often be the case that respective transmittingantennas are dedicated to respective users (respective transmissioncounterparts). In the embodiment shown in FIG. 5, it may be the case, inwhich the signal transmitted from the transmitting antenna 151-1 is asignal for the wireless receiver 100, and the signal transmitted fromthe transmitting antenna 151-2 is a signal not for the wireless receiver100. In such case, in the conventional MIMO receiver, an inverse matrixof a matrix representing the propagation path characteristic is found byadditionally aiming the signal transmitted from the transmitting antenna151-2 (or by dealing with the signals except a desired signal as aninterference component), and then the interference component is removedby multiplying this inverse matrix to separate (MIMO-separation) thesignals transmitted by the two transmitting antennas.

However, since the received signal strength of the signal transmittedfrom the transmitting antenna 151-2 is considerably low, the reliabilityin the arithmetic operation for inverse matrix is reduced. Consequently,the wireless receiver according to the present embodiment conducts theprocessing of the propagation path compensation for only the signaltransmitted from the transmitting antenna 151-1 by switching the twocircuits without conducting the MIMO separation processing to obtain thereceived signal.

Upon trying another viewpoint, this processing corresponds treating thesignal transmitted from the transmitting antenna 151-2 as mere noise andnot as interference component. Although the embodiment described aboveis presented under the considerably limited situation, as generalconsideration, the situation, in which the received signal strength ofthe interference signal component is considerably lower as relativelycompared with the desired signal component, is easily caused, when thedesired signal component of the signal received from the receivingantenna is compared with the interference signal component.

The advantageous effect of the wireless receiver according to thepresent embodiment is exhibited under such situation.

As described above, according to the present embodiment, when differentdata is respectively transmitted between a plurality of transmittingantennas and receiving antennas like MIMO communication, the receivingside select one of the propagation path compensation section and theinterference compensation section, and therefore the error ratecharacteristics in the receiving side can be improved even in thesituation where the interference compensation error is larger.

While the method for calculating an inverse matrix has been described asthe method of the interference compensation processing, the interferencecompensation algorithm also includes other algorithms (for example,maximum likelihood sequence estimation) and it is needless to point putthat other interference compensation algorithm may also be appliedthereto. Also, as shown in FIG. 6, switching between the propagationpath compensation section 103 and the interference compensation section104 may be conducted by informing the controller section 105 of thetransmission method utilized in the transmitting side. For example, inthe case where the transmitting side does not conduct the MIMOtransmission and the received signal is not multiple signal since thetransmission of data is conducted by only using one transmittingantenna, or in the case where the transmitting side has a plurality oftransmitting antennas and the identical radio signal is transmitted fromall transmitting antennas, there is a little actual profit forconducting the above-described interference compensation processing inthe receiving side. Thus, by informing the controller section 105 ofthis fact (transmission method), the controller section 105 can transmitan indication to the selecting section 106 so as to select thepropagation path compensation section 103.

Here, the transmitting side may inform this transmission method, oralternatively a configuration of analyzing the transmission method fromthe signal received in the receiving side may also be employed.

Second Embodiment

FIG. 7 is a block diagram, illustrating a configuration of a controllersection of a wireless receiver according to the second embodiment of thepresent invention.

Here, this controller section 105 a has a configuration similar to thecontroller section 105 shown in FIG. 2, and same numeral is referred tosame element, and the description thereof is omitted. The presentembodiment is characterized in that a controller section includes athreshold setting section 201.

The threshold setting section 201 is informed of a modulation level, acoding rate, a spreading factor, or a code multiplex number used fortransmission signal, and sets a threshold used in the comparativejudgement section 113 based on these values. For example, the QPSKmodulation system has better error resistance as compared with 16QAMmodulation system when the propagation path environment is deteriorated.When the QPSK is employed, by performing the propagation pathcompensation for the received signal, a probability for obtaining thedata containing no error becomes higher than the case the 16QAM isemployed as modulation system. More specifically, it is preferable tochange the reference (threshold) for selecting one of the propagationpath compensation section 103 and the interference compensation section104 in response to the modulation system of the transmission signal(modulation level). Having this configuration, the case of stopping theoperation of the interference compensation section 104 by selecting thepropagation path compensation section 103 is more frequently occurred,and therefore the power consumption of the wireless receiver is reduced.

Similar discussion can be made concerning the coding rate, spreadingfactor or code multiplex number used for transmission signal, inaddition to the modulation level. Thus, the threshold setting section201 sets the threshold used in the comparative judgement section 113 bysuitably changing thereof, in response to the modulation levels used forthe transmission signal.

Here, the modulation levels mentioned above may be informed from thetransmitting side, or obtained by analyzing the signal received from thereceiver side to provide the modulation level or the like.

As such, according to this embodiment, the switching reference used forthe transmission signal is changed according to modulation level or thelike when one of the propagation path compensation section and theinterference compensation section is switched to be employed in thereceiving side, and therefore the case of selecting the propagation pathcompensation section is more frequently occurred to provide reducedpower consumption of the wireless receiver.

The wireless receiver according to the present invention is capable ofbeing installed in the communication terminal apparatus and the basestation apparatus in the mobile radio communication system, and this canprovide the communication terminal and the base station apparatus havingadvantageous effects similar to the above-described advantageouseffects. Further, the wireless receiver according to the presentinvention can be utilized in the mobile radio communication system thatutilizes a multi-carrier system such as Orthogonal Frequency DivisionMultiplex (OFDM) or the like, and this can provide the mobile radiocommunication system having advantageous effects similar to theabove-described advantageous effects. Since the transmission systememploying the multi-carrier is set to have lower symbol rate (longsymbol length), there is an advantageous effect of reducing theinter-code interference by the multipath in the multipath environment.

In addition, the inter-code interference by multipath can also beremoved by inserting the guard interval.

As have been described above, according to the present invention, theerror rate characteristic in the receiving side even under theenvironment, in which the interference compensation error becomes largerin the receiving side, can be improved in the case of transmittingdifferent data between a plurality of transmitting antennas and aplurality of receiving antennas respectively as in the MIMOcommunication.

INDUSTRIAL APPLICABILITY

The present invention can be applied to a wireless receiver, whichreceives data transmitted in parallel from a plurality of transmittingantenna by employing a plurality of receiving antenna, and a wirelessreception method employed in such apparatus.

1. A wireless communication apparatus comprising: a plurality ofantennas; and a transmitting section that transmits a signal indicatingwhether to perform (i) multi-input/multi-output transmission thattransmits different data from respective ones of the plurality ofantennas, or (ii) data transmission that transmits data using only oneof the plurality of antennas.
 2. A wireless communication apparatuscomprising: a plurality of antennas; and a transmitting section thattransmits a signal indicating whether to perform (i)multi-input/multi-output transmission that transmits different data fromrespective ones of the plurality of antennas, or (ii) data transmissionthat transmits same data from all of the plurality of antennas.
 3. Awireless transmission method comprising the steps of: transmitting asignal indicating whether to perform (i) multi-input/multi-outputtransmission that transmits different data from respective ones of aplurality of antennas or (ii) data transmission that transmits datausing only one of the plurality of antennas; and in accordance with saidsignal, performing said multi-input/multi-output transmission or saiddata transmission.
 4. A wireless transmission method comprising thesteps of: transmitting a signal indicating whether to perform (i)multi-input/multi-output transmission that transmits different data fromrespective ones of a plurality of antennas or (ii) data transmissionthat transmits same data from all of the plurality of antennas; and inaccordance with said signal, performing said multi-input/multi-outputtransmission or said data transmission.